1. Field of the Invention
This invention relates to a moving image communication quality determination apparatus and in particular to a moving image communication quality determination apparatus for evaluating the quality of a digital image in digital moving image communications.
2. Description of the Related Art
The international standards for digital moving image code (simply, moving image code) include MPEG (Motion Picture Expert Group)-2 (ISO/IEC-13818) and MPEG-4 (ISO/IEC-14496) by ISO (International Organization for Standardization) and IEC (International Electrotechnical Commission) of international standardization organizations and H.261, H.263, etc., of ITU (International Telecommunication Union) Recommendations, for example. In the description to follow, unless otherwise specified, the moving image code refers to a moving image code conforming to the above-mentioned international standards. Alternatively, it is also applied to the moving image code based on a prediction coding technique used in the above-mentioned international standards.
For example, the main portion of xe2x80x9cDouga tuushin souchi (moving image communication apparatus)xe2x80x9d of Japanese Patent Application No. Hei 10-052531 by the present inventor (an example in a related art) corresponds to a moving image communication quality determination apparatus for evaluating the quality in communication using such moving image code. The corresponding portion relevant to the description of the invention will be briefly discussed for easy comparison with the configuration of the apparatus of the invention.
FIG. 4 is a block diagram to show a configuration example of an image processing system containing a moving image communication analysis apparatus according to the example in the related art. A transmitter 112 and a receiver 135 are connected to a network 20 for transferring digital moving image code (simply, moving image code) in real time. In the transmitter 112, a moving image encoder 110 prepares moving image code and outputs the prepared moving image code to the network 20 through a moving image transmission section 111. In the receiver 135, a moving image reception section 131 receives input moving image code and outputs the received moving image code to a moving image decoder 130. The moving image decoder 130 decodes the input image code and outputs the provided digital moving image to a display 133. The display 133 displays the input digital moving image on a display screen.
The quality of the provided digital image displayed on the display 133 from the transmitter 112 is degraded because of the following causes:
First, the causes of degradation of the image quality include a transmission error of data of moving image code, packet discard in a transmission packet group, a transmission delay of data of moving image code, fluctuation of the delay, and the like.
Next, the degradation of the image quality spreads or a fault in the moving image decoder 130 occurs and a processing failure occurs in decode processing of the moving image code. Further, the processing failure in the decode processing spreads or a fault in the display 133 occurs and display processing of the digital moving image displayed on the display screen of the display 133 may become faulty.
To maintain and improve the quality of the transmitted moving image code, it is important to evaluate degradation of the quality of a digital moving image as described above. Then, the receiver 135 comprises a code data section 132 for collecting received moving image code. A moving image communication analysis apparatus 40 is connected to the network 20 and detects degradation of the moving image code transferred in the network 20. The code data section 132 transfers with no error the collected moving image code to the moving image communication analysis apparatus 40 via the network 20. The term xe2x80x9ctransfer with no errorxe2x80x9d mentioned here refers to a method of detecting a transmission error and executing resending, etc., for transmitting data with no transmission error as a result.
The moving image communication analysis apparatus 40 outputs the input moving image code to a collected code section 402. The collected code section 402 stores the input moving image code therein. A decoding section 404 restores the moving image code stored in the collected code section 402 to the received digital moving image and outputs the provided digital moving image to a degradation component section 405.
On the other hand, the transmitter 112 transfers with no error the same moving image code held in the moving image encoder 110 as the moving image code transmitted in real time to the moving image communication analysis apparatus 40 via the network 20. The term xe2x80x9ctransfer with no errorxe2x80x9d refers to processing as described above. The same moving image code as the moving image code transmitted in real time, input to the moving image communication analysis apparatus 40 is output to an original image code section 401. The original image code section 401 stores the input moving image code therein. A decode section 403 restores the moving image code stored in the original image code section 401 to the pre-transmitted digital moving image and outputs the provided moving image restoration value (provided moving image) to the degradation component section 405.
The degradation component section 405 calculates a difference image having as new gradation values of the digital moving image the values resulting from subtracting the gradation values of pixels of the pre-transmitted digital moving image from those of the corresponding pixels of the received digital moving image. Further, in an example showing a degradation component, the sum of the squares of all pixels of the difference image is calculated, the sum of the squares of all pixels of the pre-transmitted digital moving image is calculated, and the ratio between the square sums is found and is output as a kind of parameter representing the image quality, namely, SNR (signal to noise ratio).
Next, remedies to deal with an anomaly of moving image code and an anomaly of a display in related arts to be compared with the invention will be discussed. If the moving image code input to the moving image decoder contains an anomaly, an anomaly occurs in the provided moving image, as described above. A large number of arts of using means for detecting an anomaly of moving image code for transmission and processing of the moving image code are well known.
xe2x80x9cDougazou fugouka/fukugouka souchixe2x80x9d (moving image coding/decoding apparatus) of JP-A-8-251596 by KIKUCHI Yoshihiro (kabushikikaisha Toshiba) et al. shows a processing example of detecting an anomaly from the decode value of a moving image and the range that the decode value can take. xe2x80x9cDougazou data no densou houhou oyobi densou souchixe2x80x9d (moving image data transmission method and transmission apparatus) of JP-A-7-322248 by SHINODA Mayumi (Matushita denki sangyou kabushikikaisha) et al. shows an example of detecting an anomaly of moving image code and again making a transmission request for resending the moving image code, thereby decreasing anomalies of the transmitted moving image code.
Next, anomalies occurring in moving image code transmitted via a network will be discussed in detail. First, as one of the anomalies occurring in moving image code, when an agreement of conforming to each standard as described above is made, the moving image code may contain code out of standard because of a transmission error of the moving image code, a failure of a moving image encoder, etc. If the code portion out of standard is input to a moving image decoder, the moving image decoder stops decoding the code out of standard and performs the preparation operation for detecting another normal code, then restarts decoding the normal code in the moving image code.
The decode operation of the moving image decoder will be discussed in detail with reference to FIGS. 5A and 5B, which are conceptual drawings to show the format of moving image code. As shown here, moving image code 61 is a string of bits concatenated in series in the bit order. While the moving image code 61 is read one bit at a time in the bit order, it is decoded. The current read bit is pointed to by a code pointer 62. As the decoding advances, the code pointer 62 advances on the moving image code 61. As shown in FIG. 5A, anomalous code 99 exists at one point of the moving image code 61 and when the code pointer 62 encounters the anomalous code 99, an anomaly is detected.
Since the decode value of the bits following the anomalous code is not reliable, the code pointer 62 searches the bits following the anomalous code for only predetermined synchronous code in order. As shown in FIG. 5B, synchronous code 63 exists at another point of the moving image code 61 and then the code pointer 63 encounters the synchronous code 63. At this time, the bits from the anomalous code 99 to the synchronous code 63 are all discarded and are not decoded into digital moving image. Numeral 64 denotes the discarded bits.
However, the duration required for the preparation operation until the decoding is restarted after the anomalous code is detected is not constant because of the processing timing difference in the circuitry implemented as the moving image decoder. Therefore, moving image codes input one after another by the time the decoding is restarted are not decoded and the portion of the moving image corresponding to the moving image code not decoded is lost. Further, the magnitude of the loss caused by the moving image code not decoded depends on the position of the synchronous code and therefore is not constant. The case where decoding can be restarted at the bit following the detection point of anomalous code out of standard, namely, the case where code other than code out of standard can be decoded also occurs.
Next, for example, the portion of code detected as an error based on error correction code or error checking code because of a transmission error of moving image code on a network, such as a packet, is discarded and thus a part of the moving image code is lost. The portion of the moving image corresponding to the lost code portion cannot be decoded. When the error is recovered from as described above and the subsequent code is input to the moving image decoder, some code is not decoded and the portion of the moving image corresponding the code not decoded is lost.
To produce moving image display at the same time as decoding, a coded time stamp is decoded and is collated with the time information at the point in time and if the decoding and display are not in time for the timing, display output is omitted or the corresponding code portion is discarded and is not decoded. When a packet not received within a predetermined time and delayed because of resending the packet with an error detected or network congestion or for any other reason is input to a moving image decoder, it is not in time for the display timing and an undecoded code portion occurs.
On the other hand, display anomalies occur in addition to decoding anomalies. Here, assume that pixel data by frame of a moving image provided by decoding is input to a display. If the input moving image provided by decoding is not in time for the timing at which it is to be displayed on the display, the frames before the frame in time for the display timing are discarded, namely, are not displayed.
Arts of detecting moving image code anomalies as described above are well known and are used to make a specific treatment on the moving image or resend the code.
As described above, the moving image communication quality determination apparatus in the related art finds a difference image between the original image and the degraded image on which an evaluation is to be conducted, regards the difference image as a degradation component, and uses the ratio of the square sum of the degradation component as the evaluation value of the image quality as SNR in the example.
The reason why the original image is required is that if the moving image, for example, is a rough pattern, contains a drawing like moth-eaten marks, or is an image of a contorted human face, it may be original, thus generally it is impossible to calculate a degradation component only from the degraded image. However, the method of finding a difference between the digital image provided by decoding and the original image (pre-transmitted digital image) would provide a degradation component from the original image easily and reliably.
However, the above-described method of finding a difference between the pre-transmitted and received digital images involves the following two problems in the point of data communication costs:
The first problem is the apparatus required for acquiring original image data and costs. The computer used with the moving image communication analysis apparatus in the example in the related art needs to acquire original images from a computer having a mechanism for retaining original image data, as typified by a moving image server.
Moving image data generally has an enormous information amount and transferring the moving image data between computers requires a transmission line for connecting the computers and a transfer apparatus using the transmission line. Further, for example, if use of the transmission line is chargeable and the user is charged for using the transmission line according to the use time or the communication data amount, administration costs are increased in any case.
In xe2x80x9cDouga tuushin souchixe2x80x9d of Japanese Patent Application No. Hei 10-052531 in the example in the related art, moving image code provided by coding original image data is reliably transferred from a moving image server to a computer for calculating an image quality evaluation value. Since the information amount of the moving image code is from about one third to fifth to one thirtieth to fiftieth less than that of the original image data, the communication costs can be decreased reasonably. However, the transmission line for transferring data between computers and the transfer apparatus for transferring data between computers do not become unnecessary.
The second problem is communication costs for acquiring the moving image code of the degraded image on which an evaluation is to be conducted. In xe2x80x9cDouga tuushin souchixe2x80x9d of Japanese Patent Application No. Hei 10-052531 described above, moving image code is collected at a moving image reception terminal and is reliably transferred as data to a computer for calculating an image quality evaluation value. Since the loads of the operation amount and the processing amount on the moving image reception terminal are not increased, it is easy to conduct an evaluation at a comparatively small portable terminal on which many limitations of the physical size, the weight, the power consumption amount, etc., are imposed; this is a good point. However, since the collected moving image code is transferred as data, the communication cost for transferring the data of the moving image code having the same degree of information amount as the original moving image code is required.
The problems to be solved as the related art in xe2x80x9cDouga tuushin souchixe2x80x9d of Japanese Patent Application No. Hei 10-052531 have been described.
On the other hand, according to xe2x80x9cGazou tensou hyouka souchixe2x80x9d (image transfer evaluation apparatus) of JP-A-8-22360 by BASUGI Masao (NTT) et al., a method of returning moving image code to a transmission terminal transmitting the moving image code via a specific point of a network of the moving image transmission destination is adopted. Thus, transfer of the original image data and transfer of the once received image data on which an evaluation is to be conducted become unnecessary. However, the quality of the moving image transmitted to and returned from the destination and the quality of the moving image transmitted on the one-way line to the actual reception terminal used by the user differ in the state of transmission error, transmission delay, packet discard, etc., a difference occurs in degradation of the moving image quality; the moving image quality enjoyed by the user from a display cannot actually be evaluated.
A large number of examples of instruments for measuring a packet delay transmitting moving image data, variation of the packet delay, packet discard rate, packet resending rate, packet error rate, bit error rate, etc., which will be hereinafter referred to as transmission characteristic measuring instruments, have been well known. To use the measuring instruments for measuring the degree of degradation of the image quality to evaluate real-time moving image communication, the original image or comparison image is not required, of course. However, the degradation degree as an image cannot be known; this is a problem.
Where degradation of the image quality as an image is concerned, the above-described prediction coding technique is used heavily in the transmission and reception operation of moving image code, whereby as reference values and referenced values increase, a reference value anomaly will spread. Thus, to suppress the effect of an error in moving image code, a method of avoiding heavy use of the prediction coding technique in the transmission and reception operation of the moving image code is available.
When an anomaly occurs in the code portion of important information of the image size, the format, etc., the moving image code cannot be restored to an image even if other codes are normal.
Thus, the important information of the image size, the format, etc., is scattered appropriately on the code string and if code at a specific point is anomalous, an error correction may be made using code at any other normal point or the value may be replaced. It is necessary to evaluate the degradation degree of the image quality relative to an error in transmission of moving image code or a loss of image code. However, the transmission characteristic measuring instrument cannot evaluate the degradation degree of the image quality relative to an error in transmission of moving image code or a loss of image code; this is a problem.
By the way, in xe2x80x9cDougazou fugouka/fukugouka souchixe2x80x9d of JP-A-8-251596 described above, an anomaly of moving image code is detected and decoding processing is changed, whereby degradation of the image quality is decreased. In xe2x80x9cDougazou data no densou houhou oyobi densou souchixe2x80x9d of JP-A-7-322248, an anomaly of moving image code is detected and again a request for transmitting the image code with the error detected is made for resending the moving image code, whereby spread of degradation of the moving image code is decreased.
It is necessary to perform processing so that degradation detection of moving image code is in time for the display operation while the real-time communication, decoding, and display operation is performed by changing decoding processing for the moving image code, resending the moving image code with degradation detected, etc. Thus, margins are required for the time conditions of the amount of data that can be transferred per unit time, the computer processing speed, etc. For example, as a larger number of errors occur, additional processing is increased or resending the image code with degradation detected is increased. Therefore, the actual moving image code processing amount is lessened or the transmission amount of the image code transmitted per unit time is decreased as compared with the processing or transmission amount of a moving image that can be transferred with no error.
To previously code and store a moving image, read the moving image code at the transmission time, and transmit the read moving image code at the same time, it is necessary to appropriately select parameters of the coding rate, coding parameter, coding mode, etc., at the moving image coding time and code them according to the error degree. However, in the methods shown in JP-A-8-251596 and JP-A-7-322248, the parameters at the moving image coding time vary depending on the error degree in moving image code, thus guidelines for the values of the parameters are not provided.
The coding rate refers to the amount of the moving image code transmitted per unit time in real-time transmission. Where the international standards for moving image code are concerned, the coding parameter and the coding mode specify coding conditions of moving image data. That is, for example, the coding parameter and the coding mode are the number of vertical and horizontal pixels of a screen (also called image size), the number of intensity pixels and the number of color difference pixels (also called color difference format), the number of frames per unit time (also called frame rate), coarseness of quantization, the type of interframe prediction coding technique (order of frames taking the prediction type I, P, B, etc., in MPEG), the type of any other prediction coding technique (motion vector prediction, DC/AC coefficient prediction, etc., in MPEG), etc.
The prediction types I, P, and B are the interframe prediction coding technique types and more than one time prediction mode can be selected. That is, in the interframe prediction coding technique, the moving image coding technique called prediction mode (I mode) not executing prediction based on the correlation between frames, bi-directional prediction mode (B mode), or unidirectional prediction mode (P mode) is selected for use in moving image frames. The xe2x80x9cIxe2x80x9d of the I mode denotes xe2x80x9cintra prediction,xe2x80x9d the xe2x80x9cBxe2x80x9d of the B mode denotes xe2x80x9cbidirectional prediction,xe2x80x9d and the xe2x80x9cPxe2x80x9d of the P mode denotes simply prediction. Therefore, in an encoder and a decoder conforming to one of the above-described standards, the I, P, or B mode is also selected for use in communication.
Generally, use of the B mode even for a part of a moving image requires a large processing scale, thus some machines have only the P mode function or if the B mode is selected, the P mode is used for a part of a moving image and the B mode is used for another part of the moving image. Conversely, if the P mode is selected, often the B mode is not used at all. Throughout the specification, xe2x80x9cselection of P modexe2x80x9d refers to the case where the B mode is not used and xe2x80x9cselection of B modexe2x80x9d refers to use of the P and B modes in combination.
For simplicity throughout the specification, the moving image coding technique is also used in the sense also containing selection and use of one value from among different parameters. For example, in the above-mentioned standards and recommendations, a quantization coefficient is selected from within one range of integer values. The value is used as the quantization coefficient and coding is executed, thus the moving image coding technique is contained in the sense indicating one of the moving image coding technique options.
Next, the proper use of the moving image code mode types will be discussed. Which moving image coding technique is optimum in moving image communications varies depending on the use purpose and the use situation.
The B mode has a feature of high coding efficiency and requiring a small code amount; on the other hand, the P mode has a feature of a short decode processing delay time. The code difference amount between the B and P modes varies depending on the picture material and a general tendency will be discussed. For example, the P mode with a small decode delay amount is effective for an application such as a video conference in many cases and the B mode with a small code amount may be effective for an application where the decode delay amount is allowable.
To code image data assuming that statistical relationship between portions of moving image data, the prediction coding technique is a method of coding the difference between a prediction value calculated by a calculation method determined using already coded image data and the actual value of the image data to be coded. The difference between the calculated prediction value and the actual value of the image data to be coded is also called prediction residual. The data used to calculate the prediction value is also called reference value. At this time, if the statistical nature of the image data is close to the assumed one, the prediction residual often becomes a value close to zero.
Therefore, short codes increase and it is made possible to compress the code amount. However, if the reference values are often used, when the reference value contains an error, the value of the digital image provided by decoding the image code also becomes erroneous, thus the error easily spreads. Therefore, to optimally select coding conditions, a method of finding the coding conditions applied when the quality of each received, decoded, displayed moving image is good in a state close to the actual characteristics as much as possible becomes necessary.
As described above, in the decode processing change method and the method of resending a part of the moving image code, whether or not the correspondence between the coding condition and the moving image quality under the coding condition is adequate is not known. That is, a problem of necessity for obtaining the knowledge of the correspondence between the coding condition and the moving image quality is involved.
The aforementioned problems have been raised in the related art of xe2x80x9cDougazou fugouka/fukugouka souchixe2x80x9d of JP-A-8-251596 and xe2x80x9cDougazou data no densou houhou oyobi densou souchixe2x80x9d of JP-A-7-322248.
It is therefore an object of the invention to provide a moving image communication quality determination apparatus that can evaluate the quality of a moving image input to a receiver via a network from a transmitter in the field without transferring image data of an original image or moving image code.
According to a first aspect of the present invention, there is provided, in a moving image communication system comprising a network and a moving image server connected to the network wherein the moving image server transmits digital moving image code via the network, a moving image quality evaluation determination apparatus comprising means being connected to the network for receiving the digital moving image code, means being connected to the network for detecting an anomaly of the digital moving image code, and image quality evaluation value calculation means being connected to the network for calculating the degree of quality degradation in a digital moving image caused by the detected anomaly.
According to a second aspect of the present invention, in the moving image quality evaluation determination apparatus, the receiving means comprises means for decoding a portion of the digital moving image code not containing the detected anomaly into a digital moving image.
According to a third aspect of the present invention, in the moving image quality evaluation determination apparatus, the anomaly detecting means detects a transmission error of the digital moving image code in the network and discard of the digital moving image code as the anomaly of the digital moving image code.
According to a fourth aspect of the present invention, in the moving image quality evaluation determination apparatus, the anomaly detecting means detects a transmission time delay of the digital moving image code in the network as the anomaly of the digital moving image code.
According to a fifth aspect of the present invention, in the moving image quality evaluation determination apparatus, the anomaly detecting means detects the fact that the digital moving image code to be decoded by the means for decoding the code into a digital moving image is not predetermined digital moving image code as the anomaly of the digital moving image code.
According to a sixth aspect of the present invention, in the moving image quality evaluation determination apparatus, when in decoding a specific part of the digital moving image code, the decode value of a different portion is referenced, the anomaly detecting means detects an anomaly of the decode value of the different part spreading to the decode value of the specific part of the digital moving image code as the anomaly of the digital moving image code.
According to a seventh aspect of the present invention, the moving image quality evaluation determination apparatus further includes means for locating an image area corresponding to the detected anomaly in the digital moving image, wherein the image quality evaluation value calculation means outputs the size of the anomalous image area or a size ratio of the anomalous image area to the whole as the calculation result.
According to an eighth aspect of the present invention, in the moving image quality evaluation determination apparatus, the image quality evaluation value calculation means calculates the size of the anomalous image area or a size ratio of the anomalous image area to the whole in pixel units of the digital moving image.
According to a ninth aspect of the present invention, in the moving image quality evaluation determination apparatus, the image quality evaluation value calculation means calculates the size of the anomalous image area or a size ratio of the anomalous image area to the whole in units of small areas into which a screen is divided in a specific range.
According to a tenth aspect of the present invention, in the moving image quality evaluation determination apparatus, the image quality evaluation value calculation means calculates the size of the anomalous image area or a size ratio of the anomalous image area to the whole in displayed frame units.
According to an eleventh aspect of the present invention, in the moving image quality evaluation determination apparatus, the image quality evaluation value calculation means sets the gradation value of the anomalous image area detected by the means for locating an image area corresponding to the detected anomaly in the digital moving image to zero, calculates a first square sum of the gradation value of the anomalous image area and a second square sum of the gradation values of the whole, calculates a ratio between the first and second square sums, and outputs the calculation result as an image evaluation value.
According to a twelfth aspect of the present invention, in the moving image quality evaluation determination apparatus, the image quality evaluation value calculation means corrects by concealment the gradation value of the anomalous image area detected by the means for locating an image area corresponding to the detected anomaly in the digital moving image, calculates a first square sum of the gradation value of the anomalous image area corrected and a second square sum of the gradation values of the whole, calculates a ratio between the first and second square sums, and outputs the calculation result as an image evaluation value.
According to a thirteenth aspect of the present invention, in the moving image quality evaluation determination apparatus, when in decoding a specific part of the digital moving image code, the decode value of a different portion is referenced, the anomaly detecting means detects an anomaly of the decode value of the different part spreading to the decode value of the specific part of the digital moving image code based on the code corresponding to the detected anomaly and the means for locating an image area corresponding to the detected anomaly in the digital moving image locates the image area containing the specific part of the digital moving image code corresponding to the spreading anomaly.
According to a fourteenth aspect of the present invention, in the moving image quality evaluation determination apparatus, the means for locating an image area corresponding to the detected anomaly in the digital moving image comprises a storage section allocated in a fixed length of one bit or more per pixel and records the anomalous area in the storage section.
According to a fifteenth aspect of the present invention, in the moving image quality evaluation determination apparatus, the means for locating an image area corresponding to the detected anomaly in the digital moving image comprises a storage section allocated in a fixed length of one bit or more per small area into which a display screen is previously divided and records the anomalous area in the storage section.
According to a sixteenth aspect of the present invention, in the moving image quality evaluation determination apparatus, the means for locating an image area corresponding to the detected anomaly in the digital moving image specifies a rectangular area on a display screen and records maximum and minimum values of column and row numbers of the rectangular area on the display screen.
According to a seventeenth aspect of the present invention, in the moving image quality evaluation determination apparatus, the means for detecting an anomaly of the digital moving image code is a decoder and the decoder detects input digital moving image code being undecodable, outputs an error at the detection time, detects a mark indicating code synchronization of the next digital moving image code, and restarts decoding this digital moving image code.
According to an eighteenth aspect of the present invention, in the moving image quality evaluation determination apparatus, the means for detecting an anomaly of the digital moving image code is a decoder and the decoder detects the presence or the absence of a processing delay of transfer time of the digital moving image code in the network, outputs an error at the detection time of a processing delay, detects a mark indicating code synchronization of the next digital moving image code, and restarts decoding this digital moving image code.
According to a nineteenth aspect of the present invention, in the moving image quality evaluation determination apparatus, the means for detecting an anomaly of the digital moving image code is a display and the display detects an anomaly making it impossible to display on display means for each frame.
According to a twentieth aspect of the present invention, the moving image quality evaluation determination apparatus further includes means for storing the quality evaluation value of the calculation result of the quality degradation degree in the digital moving image every plurality of digital moving images, and means for transmitting the quality evaluation value asynchronously to the digital moving image through the network.
According to a twenty-first aspect of the present invention, the moving image quality evaluation determination apparatus is built in a receiver being connected to the network for receiving the digital moving image.
According to a twenty-second aspect of the present invention, the moving image quality evaluation determination apparatus is built in a repeater being connected to the network for relaying transfer of the digital moving image.
The image area means an image and is an area inside the closed contours on a two-dimensional screen comprising pixels arranged. For example, each hatched portion in squares in FIGS. 2B, 2C, 3B and 3C is one image area. It can be located based on contour or quadrangle apex positions and can also be located by specifying all pixels contained in the area by positions or numbers.